Stabilization of Pt Nanoparticles Due to Electrochemical Transistor Switching of Oxide Support Conductivity

Polymer electrolyte fuel cells (PEFCs) offer an efficient way of chemical-to-electrical energy conversion that could drastically reduce the environmental footprint of the mobility and stationary energy supply sectors, respectively. However, PEFCs can suffer from severe degradation during start/stop events, when the cathode catalyst is transiently exposed to very high potentials. In an attempt to mitigate corrosion of conventional carbon support materials for Pt catalyst nanoparticles under these conditions, conductive metal oxides like antimony-doped tin oxide (ATO) are considered alternative support materials with improved corrosion resistance. A combined in situ anomalous small-angle X-ray scattering and post mortem transmission electron microscopy study reveals PEFC-relevant degradation properties of ATO-supported Pt in comparison to carbon-supported Pt catalysts. Against expectation, the superior stability of ATO-supported Pt nanoparticles cannot be merely explained by improved support corrosion resistance. Instead, the dominant loss mechanism of electrochemical Ostwald ripening is strongly suppressed on ATO support, which can be explained with a potential-dependent switching of support oxide surface conductivity. This electrochemical transistor effect represents an important design principle for the development of optimized metal oxide support materials that protect supported Pt nanoparticles at high potentials, where careful consideration of the metal oxide flat-band potential is required in order to maintain high catalyst performance at normal PEFC cathode operation conditions at the same time.